Some speech recognition systems attempt to classify portions of an audio signal as speech. These systems may then selective transmit the portions that appear to be speech to a speech decoder for further processing. Speech recognition systems may attempt to classify the portions of an audio signal based on an amplitude of the signal. For example, the systems may classify a portion of an audio signal as speech if the portion has a high amplitude.
Classification schemes may operate on an assumption that speech is more likely to have a higher amplitude than that of noise. However, loud background noises or significant interference of the audio signal caused by a device in the transmission chain may generate noise with a high amplitude. In these cases, a classification scheme that relies upon signal amplitude may misclassify frames that contain noise as containing speech.